It is well known that in electrical power transport equipment, such as high voltage or extra high voltage cables, there exists, at the level of the cable connection zones, such as in cable joints, cable branching or connection to cells or transformers, a discontinuity of the electrical field adjacent the end of the cable shielding. When the electrical discontinuity or potential gradient exceeds a predetermined value along the surface of the unshielded electrical conductor insulator surrounded by a gas, such as the air, gas discharges may occur which generate ozone and other gases which can affect greatly the electrical insulating equipment. To prevent such drawbacks, use in generally made at the level of the cable shielding interruption of cone-shaped termination equipment or deflective cones including or not condensers, which generally show outer dimensions far greater than the proper cable terminator, more particularly on extra high voltages. Said deflective cones have to be arranged within procelain insulators filled with an insulating material, thereby leading to problems in handling and connecting said integers in situ.
It is also known to make use for low voltage cables of materials exhibiting non-linear resistance characteristics, high permittivity materials and carbon black-based materials having a calibrated resistance. French application No. 2,423,036 to the assignee discloses a self-blending mastic compound containing silicon carbide particles of a calibrated constant granulation or grain-size disposed at the level of the shielding end so as to extend onto the outer surface of the unshielded conductor insulator along a required distance to prevent electric discharges and to obtain the desired electrical characteristics at the termination end. Said different products show, however, limited performances as a result of heating in over-voltage conditions, and there are no hints to utilize same for manufacturing efficient electrical stress reduction or control electrodes on high voltages, nor particularly on extra high voltages.
On the other hand, in manufacturing cable terminators, it has been proposed to substitute pre-manufactured junction equipment assemblies of synthetic rubbers for the insulators of glass, porcelain or epoxy resins, thereby facilitating handling and mounting in situ. However, said junction equipment assemblies show limited electric performances, as also the junctions and the branching equipment where moulded cast iron boxes have been replaced by ribboned or cold-casted resin assemblies.